This invention relates in general to a fabrication process and more specifically, to a process for fabricating a flexible electrophotographic imaging member.
Flexible electrophotographic imaging member belts are usually multilayered photoreceptors that comprise a substrate, an electrically conductive layer, an optional hole blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer and, in some embodiments, an anti-curl backing layer. One type of multilayered photoreceptor comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. U.S. Pat. No. 4,265,990 discloses a layered photoreceptor having separate charge generating (photogenerating) and charge transport layers. The charge generating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
One of the more encouraging advances in electrophotographic imaging which has emerged in recent years is the successful fabrication of a of a flexible imaging member which exhibits a nearly ideal capacitive charging characteristic, outstanding photosensitivity, low electrical potential dark decay, and long term electrical cyclic stability. This imaging member design employed in belt form usually comprises a substrate, a conductive layer, solution coated hole blocking layer, a solution coated adhesive layer, a thin vapor deposited charge generating layer of pure organic pigment, a solution coated charge transport layer, a solution coated anti-curl layer, and an optional overcoating layer. For example, in U.S. Pat. No. 4,587,189 to Hor et al photoconductive imaging members are described comprising a vacuum sublimation deposited benzemidazole perylene charge generating layer for electrophotographic imaging members.
This multilayered belt imaging member provides excellent electrical properties and extended life, but is also observed to exhibit a major problem of forming cracks in the charge generating layer. Since these cracks have an appearance similar to cracks found in dried mud flats, they are often referred to as "mud cracks". These observed mud cracks in the charge generating layer are a two-dimensional network of cracks. Mud-cracking is believed to be the result of built-in internal strain due to the vacuum sublimation-deposition process and subsequent solvent penetration through the thin charge generating layer. The penetrating solvent dissolves the adhesive layer underneath the generating layer during application of the charge transport layer coating solution. Crack formation in the charge generating layer seriously impacts the versatility of a photoreceptor and reduces its practical value. Cracks in charge generating layers not only print out as defects in the final copy, but may act as strain concentration centers which propagate the cracks into the other electrically operative layer, i.e. the charge transport layer, during dynamic belt machine cycling.
While the above described imaging member exhibits desirable electrical characteristics, there is an urgent need to resolve the cracking issue in order to achieve an imaging member capable of forming high quality prints under extended image cycling conditions. It is also important that any solution employed to solve the charge generating layer mud-cracking problem does not produce any deleterious effects on the electrical and mechanical integrity of the original device.
Thus, there is a continuing need for an electrophotographic imaging member having improved resistance to mud crack formation in the charge generating layer.